Conventionally, it is known that an optical module that converts an electrical signal into an optical signal is mounted in a transponder unit used for optical communications. Further, it is known that the transponder unit downloads software data of the optical module to the optical module by using an inter-integrated circuit (I2C) interface disposed in the optical module. Hereinafter, this function is referred to as “module download.” When the software of the optical module is revised, the transponder unit can update the optical module by performing the module download in a state in which the optical module is mounted in the transponder unit.
The module download of the conventional technology will be described below with reference to FIG. 8 and FIGS. 9A to 9C. FIG. 8 is a diagram for explaining an example of the conventional data transmission technique. FIGS. 9A to 9C are diagrams illustrating an example of the conventional communication format of I2C communication. Further, FIG. 8 illustrates an example in which I2C communication is performed between an I2C command transmission unit and an I2C command processing unit that are disposed in the transponder unit.
First, as illustrated in FIG. 8, the I2C command transmission unit transmits a data transmission command (CMD A) and software data (data) to the I2C command processing unit (step S1: write command). Specifically, as illustrated in FIG. 9A, the I2C command transmission unit transmits Add+W (Address+Write bit) 10, CMD A 12, LENGTH 14 representing the data length, DATA 16-1 to DATA 16-n, and CHK (CHECK) 18 representing a check bit to the I2C command processing unit.
Next, as illustrated in FIG. 8, the I2C command transmission unit transmits a read command for receiving a response signal from the optical module to the I2C command processing unit (step S2). Specifically, as illustrated in FIG. 9B, the I2C command transmission unit transmits Add+R (Address+Read bit) 20 to the I2C command processing unit. Next, the I2C command processing unit transmits a response signal to the I2C command transmission unit in response to the read command (step S3). Specifically, as illustrated in FIG. 9C, the I2C command processing unit transmits MODULE STATUS 30 representing a command processing status of the I2C command processing unit, LENGTH 32 representing the data length, and CHK 34 representing a check bit to the I2C command transmission unit. In the conventional module download, all of the software data serving as a download target is downloaded to the optical module by repetitively performing step S1 to step S3.
Further, it is known that the transponder unit not only performs the module download but also periodically collects information for monitoring the occurrence of an abnormality of the optical module (hereinafter, referred to as “alarm monitor information”) from the optical module by using the I2C interface. That is, the transponder unit collects the alarm monitor information by transmitting a command for collecting the alarm monitor information from the optical module (hereinafter, referred to as “alarm monitor information collection command”) to the optical module. The transponder unit can detect, for example, the occurrence of an abnormality of an output wavelength of the optical module or the occurrence of an abnormality of output power of the optical module by periodically collecting the alarm monitor information from the optical module (see, for example, Japanese Laid-open Patent Publication No. 2008-113207)
However, the conventional technology does not consider reducing a time for the module download while performing monitoring of the alarm monitor information of the optical module.
That is, the transponder unit performs collection of the alarm monitor information even during the module download as well as during a typical operation of the transponder unit. In order to perform collection of the alarm monitor information during the module download, the transponder unit alternately transmits the data transmission command for transmitting the software data to the optical module and the alarm monitor information collection command to the optical module. The alternate transmission of the data transmission command and the alarm monitor information collection command increases the time for the model download process.
Meanwhile, in order to reduce the time for the module download, transmission of the alarm monitor information collection command may be omitted. However, in this case, the transponder unit does not collect the alarm monitor information during the module download. Thus, even if an abnormality occurs in the output wavelength or the output power of the optical module, the transponder unit cannot detect the abnormality and cope with the abnormality of the optical module. As a result, there is a likelihood that the abnormality of the optical module may, cause a failure in other circuits (channels), and thus it is undesirable.